Method of insulating conductors.



I. B. SPEED.

METHOD 0E INSULATING CONDUCTORS.

Patented Dot. 3,1916.

I flu/enrol.- James 5. Speed b APPLICATION FILED MAR-11,1915.

W/Tn eases 3. 71 Ma UNITED STATES PATENT OFFICE.

JAMES BUCKNER SPEED, OF WESTNEW BRIGHTON, NEW YORK, ASSIGNOR, Z BYASSIGNMENTS, TO WESTERN ELECTRIC COMPANY, INCORIEORATED, A. CORPORA-TION OF NEW YORK.

duction of an insulating covering for conductors which shall possess ahigher dielectric strength than coverings heret'ofore employed and whichwhen applied to the conductor will permit of the winding or coiling ofsuch conductor about small diameters without impairing the dielectricstrength of the covering.

In accordance with this invention, an insulating covering comprisingalternate layers of some of the commercial forms of insulating compoundand mica or some similar form of insulating material of similarcharacteristics is applied to the conductor.- Preferably the insulatingcompound is applied to the conductor in a tacky or sticky condition andthe mica is applied thereto in the form of finely divided particles ordust. The mica may be floated upon the conductor by passing theconductor through a chamber in which said mica particles are floating. I

While it has been possible to successfully insulate conductors with arelatively thin coating of known commercial forms of compound, such forexample as described in the Holmes and Harris Patent No. 1,101,281, andsimilar compounds, and obtain an insulated conductor which could bewound about small diameters without affecting the high dielectricstrength of the insulating passes.

coating, still when increasing the thickness of the coatings of suchinsulating 'com- .pounds to greatly increase the dielectric strength,such heavily insulated conductors could not be wound about smalldiameters without having a deleterious effect upon the dielectricstrength of such insulating coating. An insulated conductor embodyingthe present invention overcomes the defects of telile insulatedconductors heretofore produc Specification of Letters Patent.

Patented Oct. 3, 1916.

This invention will be more fully under stood by reference to theaccompanying drawing which illustrates one embodiment of the invention.

In the drawing, there is shown one form of apparatus by means of which aconductor may be insulated according to the present invention.

5 represents a furnace through which a conductor '6 passes. This furnacemay be and preferably is similar to that shown in the Holmes and HarrisPatent No. 1,101,281. The ,wire 6 passes from a supporting spool 7,under a guide 8, over and 'under one of a series of pulleys 9 which aremounted on a shaft supported in a trough 10 containing an insulatingcompound. From a pulley 9, the conductor passes up through the furnace 5and over one of a series of pulleys 11 and then down under anotherpulley 9 and up through the furnace 5, this cycle being repeated untilthe insulation is of the desired thickness. When the insulation is ofsuflicient thickness, the insulated conductor is passed'from the furnace5 over one of a series of guides 12 and is wound on a spool 13.

20 represents a chamber connected with the furnace 5 by means of pipes21 and 22. The fans 23 and 24 cause a circulation of air in thedirection indicated by the arrows. In the bottom of the chamber 20 thereis placed a quantity of mica dust which is agitated in any suitablemanner, such for example as a hammer 25 intermittently tapping thebottom of the chamber 20. By a constant agitation of the mica dust andwith a circulation of air in the chamber 20 and the furnace 5, the airin the furnace 5 between points opposite the pipes 21 and 22 will beladen with mica dust. There are openings 30, 30in the top and bottom ofthe. furnace 5, through which the conductor In order to prevent the micadust from getting into the room through these openings 30, 30 andunavoidable cracks elsewhere in the furnace 5 and the chamber 20,

the pressure of the entire system is kept just particles or Thisconductor 6' passes through the insulating compound (preferably that derscribed in the Holmes and Harris Patent No. 1,101,281) in the trough 10,and then 6 up through the furnace 5. As the coated conductor enters thefurnace 5, the coatingon the conductor is in a plastic, sticky or tackycondition, so that when the coated conductor encounters the mica laden10 air, in the furnace 5, particles of mica will attach themselves tothe coating on the conductor. form of flat particles or flakes, and itis preferable that the long diameter of these flakes be less than onefourth of the diameter of the conductor'which is being insulated, inorder that the insulated conductor shall not be rough. It is a wellknown fact that any flat particle propelled through the air withoutgyrostatic action tends to travel through the air flatwise rather thanedgewis'e. It will be seen then that the particles of mica, 'inattaching themselves to the sticky coating on the conductor, will attachthemselves flatwise, thus forming a fish-scale covering over the coatingof insulating compound. As the conductor having a coating of insulatingcompound and a covering of mica particles passes through the furnace,the coating of "insulating compound is hardened and the particles ofmica become firmly attached to I the coating of insulating compound. An-

other coating of insulating compound and then another covering ofparticles of mica may now be applied to the previously cov eredconductor and again subjected to the The mica dust is in the hardeningprocess. The number of layers,- of insulating compound and mica neededon a conductor depends upon the dielectric 40 strength desired. In orderthat the finished .insulated conductor may be smooth it is desirablethat thecl'ast layer of insulation applied be a layer of the insulatingcompound. I I

"When a conductor which has been insulated according to the presentinvention is wound about small diameters, the insulating compound-maycrack, but the particles of mica prevent the forming of a continuous 5crack' or opening from the outside of the entire covering to theconductor. It will be seen therefore that whereas the cracking of theinsulation on conductors heretofore produced materially lowers thedielectric strength, cracking of the insulating 'compound ma take placeon insulated conductors er'nbo ying the present invention, withouthavingany deleterious efiect upon the dielectric strength.

What is claimed is:

The method of insulating a conductor which consists in coating aconductor with w an insulating compound, covering the coated conductorwith particles of mica while the insulating compound thereon is in atacky condition,and baking the covered conduc tor while applying themica.

In witness whereof, I hereunto subscribe my name this 10th day of March,A. D. 1915.

. JAMES BUCKNER SPEED. Witnesses:

E. Emma, K. L. Sum;

